Process for the solvent extraction of aromatics from hydrocarbon mixtures



Feb. 17, 1959 G. R. BROWN. JR. ET AL PROCESS FOR THE SOLVENT EXTRACTION OF AROMATICS FROM HYDROCARBON MIXTURES Filed June 1,

m/zl v PHENYL ETHANOL AMINE 8 HEAT EXCHANGER mOPQ mkXm DIETHYLENE GLYCOL m HYDROCARBON DISTILLATE LIGHT FIG. I

.mm m JF m QWE V.- NNAR E EWR OC mR O. BRO) 1 RD A. RD W E"/ GRa B x. DIETHYLENE GLYCOL FIG 2 United States Patent *"2,s74,11 6- f u p K PROCESS on. THE SOLVENT EXTRACTION, 10F

AROMATICS FROM H DRQ A Glenn RL'Brown; Jii, Cleveland, and Harold'KrStreclier,

Bedford, 0hio," and Richard R; Crawford,- 'Buflalo; t N. Y assig'nors to The Standard Oil 'Company, Cleveland, Ohio, a corporation of Ohio produced by thecatalyticreforming o'f h'avy naphtha,

a mixture ofparaflinic-and napthenic hydrocarbons boiling in the range of about 200 -F;toabout-400 The unleaded F-1 octane number '-of -hydrocarbon'lstocks produced by-catalytic reformingmay yarybetvveen-about 8O and- 95, but--a-stoclewhi'cli is particularly suited to the practice of this invention has number of about Catalytrc reforming ls-aprocess which istoday vvidely practiced in '-the petroleum -industry and the object of an i unleaded octane that process is the production-of aromatic compounds from napthenlc andotherhon-aromatic"ingredieiits of heavy naphtha by-acombination-of-isomerization and dehydrogenation.-- -Thecatalytic-reformingprocesses are usuallyconducted at an elevated temperature andfpressure in-the presence-of-a catalyst -inra'hydrogen atmos- 5-5;

phere. One type of catalyst -which "is" widely" used in such processes contains-platinum 'asthe'principal active ingredient.

tion is haracterized by an octane number inthe range gasoline;

I The product of a-catalytic reformingoperaof about 80 to 95 and his suitable for use infrnotor operation'does; not completely convert-the heavy naphtha feed into aromatic compounds.uhderthe usual operating conditions; and; the aromaticsx which are produced by t the reforming .operatiomare diluted .by...th'e presencein the product of paraflinicand vother non-aromaticcompounds.

Accordingly, ,when, thel'obje'ct of the rca talytictreforming process. istthe production of relatively. pure aromatic conn pounds; ,it is necessary ,to. concentrate the aromatic-portion of the product of the icatalyticreforming operation;

A.;similarlsituation prevailsawhen the roduct ofthe cat- 2,874,116 Patented Feb. 17, 1959 alytic reforming operation is who used as a motorfuel and only the highest octane ingredients of the product are desiredp i v o= I Y Thesart hassuggested a number of methods for improving the octane number of naphthas ing'eneral, and in particular, the products of the catalytic reforming operatiom =A number of these methods involve the solventextraction of the naphtha or catalytic reformate whereby the-aromatic content of the stock treatedtis selectively removed and separated from the non-aromatic ingredients. One such process Which has' been suggested bythe prior art=is described in U. S. Patent No. 2,302,383 to-Stratford. This patent-describes a process in which naphtha is-upgraded by solvent extraction with dihydric alcohols having at least'one e ther' groupg as forexample, di-

ethylene glycol, triethylene glycol, and 1 tetraethylene lycol. 1 The dihydric glycols, While they possess a-very high degree 7 ofselectivity in 1 separating aromatic compounds fromparaffinic' compounds; ha've the disadvantage that aromatic hydrocarbons are not readily solubleptherein and "consequently considerable quantities of the glycols must bejteinployed in order to efiect an appreciable sepa'ration of the aromatic compounds. The high solvent to oil'ratio-"Which isrequired in processes employing dihydric glycolsmakes; these processes expensive; both as to capital costs and operating costs. The capital costs are" expensive because of the large equipment that "is necess'ary to"accommodate therequired' volumesofthe poundsr Among the hydroxyamines disclosed' is; phenyl ethanolaminert t a *Hydroxya'rnines"have a disadvantage when employed as a solvent in the extraction 'of' light hydrocarbon distillates' in that they no" not possessa a -great degree of selectivity" foraromatic hydrocarbons. Cons'e'quentlyfa practical increase in the aromatic content of a hydro-j carbon mixture cannot be obtained with hydroxyarnines underpractical'operating conditions. 9 t Accordingly, one of the-objects of'this invention is'to provide ant improved process for the production of an aromatic enriched; fraction from ahydrocarbon mixture containing aromaticswhich avoids the disadvantages of; the prior art. i i

*It-is another object of this invention to provide a sol vent extraction process for the recovery" of aromatics fromihydrocarbon mixtures which doesnot require high solvent'tooilratios. it v Still another obj ect' of this invention is to provide -a process for the production of a high octane gasoline from a lower octane product of a catalytic reforming operation. More especially, it is an object of this invention to provide a process whereby a gasoline having an octane number of 100 or above may be obtained from a gasoline having an octane number below 90, and in particular, to provide a solvent extraction process whereby at least a 10% yield of at least 100 octane gasoline may be obtained from a gasoline having an octane number of at least 85.

In order to facilitate an understanding of this invention, a patent drawing is attached hereto in which Figure l is a schematic flow diagram illustrating the method of this invention, and Figure 2 is a graph illustrating the improved results obtainable by means of this invention.

In brief, this invention is a process comprising the steps of extracting a liquid hydrocarbon mixture containing an appreciable quantity of aromatic compounds under conditions which will produce a separate rafiinate and extract consisting of a solvent-oil mixture with a solvent consisting essentially of a mixture. of diethylene glycol and phenyl ethanol amine, and the step of separating an aromatic enriched hydrocarbon mixture from said solvent-oil mixture.

The improved results obtainable by the method of this invention are principally attributable to the solvent employed. As pointed out above, the solvent is a mixture consisting essentially of phenyl ethanol amine and diethylene glycol. However, all combinations of these ingredients are not suitable for the purposes of this invention. In order to obtain the advantages of this invention, the solvent must contain at least 5% by volume of both ingredients. This limitation is imposed on the mixture by reason of the fact that as the composition of the mixture approaches either pure phenyl ethanol amine or diethylene glycol, the solvent mixture approaches the properties of the pure compounds. On the other hand, a mixture containing at least 5% of both ingredients exhibits unexpected and surprising improvements in solvent behavior, both as to selectivity for the aromatic compounds and as to the solubility of such compounds in the solvent, which cannot be predicted from the properties of either of the pure ingredients. It has been found that the inclusion in the solvent mixture of small amounts of water, i. e., below about by volume, will not have a detrimental effect on the solvent and in some instances will produce beneficial effects.

The procedure to be followed in carrying out the method of this invention will be better understood by reference to Figure 1 of the attached patent drawing. A hydrocarbon distillate is conveyed by means of a pump 10 and conduit 11 to a packed extraction tower 12. Any of the conventional tower packings may be employed in tower 12. While the extraction zone is shown on the drawing as the tower 12, any of the conventional equipment employing one or more theoretical extraction stages which is available for liquid-liquid extraction may be employed, for example, a centrifugal extractor. The light hydrocarbon distillate is contacted in the extraction zone with a mixture of phenyl ethanol amine and diethylene glycol which is introduced into the extraction zone by means of the pump 13 and conduit 14. A raffinate which is predominantly parafiinic in nature is produced in the extraction zone and leaves the tower 12 by means of the conduit 15. The final disposition of the rafiinate is not important to this invention, but it may be recycled to the catalytic reforming operation. The extract which is a solution of hydrocarbon richer in aromatics and solvent is conveyed from the extraction zone through the conduits 16a and 16b to the fractionator 17. The fractionator 17 is equipped with the usual re-boiler 19 which is connected to the tower by means of the conduit 20. Stripping steam may be added to the fractionator 17, if'desired, by means of the conduit 18. The extract is separated into two fractions within the fractionator 17. One fraction ,4 s a hy ro a bo st e m which i e ri h d in arom t cs and this fraction leaves the fractionating zone by means of the conduit 21. The other fraction is the mixture of phenyl ethanol amine and diethylene glycol, and this mixture is returned to the extractor 12 by means of the conduits 22a and 22b, pump 13 and conduit 14. The fractionated solvent mixture should be cooled before return to the extractor 12 and the cooling may be conveniently accomplished in heat exchanger 23 where the heat extracted is employed to heat the extract phase removed from extractor 12. The fractionator 17 may be any of the conventional fractionating apparatus such as, for example, a bubble cap tower. The fractionation zone may be operated either under pressure or under vacuum. In the latter instance, conventional equipment (not shown) is employed to produce the vacuum in a manner which is well understood in the art.

While in the above description of this process, fractionation has been disclosed as a method whereby the solvent mixture may be recovered from the extract, the invention broadly encompasses any method of solvent recovery. For example, fractional crystallization might be utilized.

A number of experimental runs were made in order to illustrate the improvements obtainable by the method of this invention. All of the extractions reported herein were conducted under atmospheric pressure and the procedure shown on the patent drawing and described above was followed. The stock employed in the experimental work was a commercial stock produced by the Platforming process, a commercial catalytic reforming process, and it had the properties reported in Table I.

TABLE I Composition of feed stock API gravity at 60 F 48.8 Specific gravity .7849 Bromine number 1.61 Kattwinkel number 51 Percent aromatics 44.8 Percent olefins 1.2 Percent saturates v 54.1 Octane number (F-l clear) Engler distillation:

IBP .165 5 200 10 216 20 231 30 244 40 p 255 50 270 60 284 70 300 80 p 320 348 373 E. P 420 Dist 98.2 Res 0.8 Loss 1.0

The data obtained in the various experimental runs are reported in Table II. In this table, phenyl ethanol amine and diethylene glycol are designated as PEA and DEG respectively. The solvent to oil ratios reported represent the volume ratio of solvent mixture to hydrocarbon which is introduced to the extraction zone. -Octane numbers reported in this table and throughout this specification are the clear F-l numbers which are obtainedfby a method well understood in the art. The yields reported represent the volume per cent of the feed which .is recovered from the aromatic enriched extract. TableHfollowsz;

TABLE II Solvent Oompo- Extrac- Solvent Yield, Octane Example sltlon, Volume tion Tem-' to 011 Volume Number Number Percent perature, Ratio Percent of Prod- F. not

1 100% PEA 130 0.43 13.9 90.4 2 100 130 1.0 26.8 95.5 130 2.3 39.0 93.3 130 0.1 0.4 103.3 .130 0.25 .9, 103.3 130 0.43 1.3 1 ;103.3 130 --1..0 3.5 103.3 130. 2.3. 4.3 103.3 130 0.1 .1 105.2 7 130, 0.43 3.7; 104.4 70%510'11-3091, :130 1.0 "13s 1035 70% grin-30% 130 g "253 31.2 102.3 0% 111-5 1 301 "0.' 1'; ."13 105.0 50% A-50% 130 0.43 I 0.9 1040 50% PEA-50% *130 1.0 11.4 103.2 50%EP3A50% 130 2.3 31.3 102.0 30% PEA-70% 130 0.1 1. 3 104. 7 DEG; 1-.

30% PEA-70% 130 0. 43 4.3 104.0

30% A'70%- 130 f 1. 0 9.4 104.0 30% PEA-70% 130 2.3 I 21.2 103.5

DEG. 50% PEA-50% 200 2.3 37. 7 95. 1

DEG. 30% PEA-50% 250 a l 2.3"; 40.4 93.3

70% PE'A30% 100 i 0.43 7.9 ;100.2 70% Pen-30% 100 1. o 10. 4 93. 4

DEG. 70%A30% 100 2. 3 32. 3 91. 5 20 50% PEA-50% 100 0.43 3.3 101.7

DEG. 27 50% PgA-50Z, 100 1.0 12.1 100.6 30% PgA-30% 100 2. 3 2a. 3 100.2 30% Pun-70% 100 0. 43 4. 2 103. 0 30% PEA-70% 100 1. 0 9.1 101. 2 30% PEA-70% 100 2. 3 13. 0 100.3

DEG.

The data reported for Examples 1-8 in Table 11 illustrate the shortcomings and deficiencies of the solvents suggested by the prior art. Examples 1-3 show that when pure phenyl ethanol amine is employed as the solvent, the aromatic content of the product, as indicated by the octane number, is improved, but not to the extent desired. The data reported for Examples 1-3 also illustrate the fact that increasing the solvent to oil ratio does not improve the quality of the product, but on the contrary, as the solvent to oil ratio is increased, the concentration of aromatics in the product tends to approach the concentration of aromatics in the feed.

Examples 4-8 plainly indicate that while diethylene glycol is capable of producing a high quality product in a solvent extraction process, the yield of the product is poor. Extrapolation of this data indicates that commercial yields of products could be obtained with diethylene glycol only if high solvent to oil ratios are employed, i. e., on the order of 6-l0zl. One of the principal advantages of our invention is that such high solvent to oil ratios are not required. a

From a study of the data reported in Table II, we have concluded that the best mode contemplated by us of carrying out our invention embodies a solvent extraction processcarried out according to the procedure described herein above in which the solvent mixture is a 50-50 mixture of phenyl ethanol amine and diethylene glycol and the extraction temperature is 130 F., while the solvent to oil ratio is 2.3 1.

Considering this invention in its broadest aspect, we contemplate employing solvent mixtures consisting essentially of at least 5% by volume of phenyl ethanol amine and 5% .by volume of diethylene glycol. Solvent mixtures containing 50% or less of diethylene glycol are preferred. However, mixtures containing as much as diethylene glycol and only 5% phenyl ethanol amine have been found to offer considerable improvement in the extraction process as compared to the pure diethylene glycol.

The temperature at which the extraction is carried out is not critical so long as a temperature is employed which will result inseparable extract and rafiinate phases .in the extraction step. However, it is preferred .to employ temperatures in the range of about 100. to 175 F.

- =.The solvent to oil ratios which maybe employed in thefmethod of this invention. are likewise not. critical. However, low solvent to oil. ratios produce :lower yields of products whereas high solvent to oil ratios impose handling and separation problems which adversely-afiect theeconomics of this process. Accordingly, it is preferred to employ solvent to oil ratios in the range of about 0.25 toabout 4.0. 1

1 A better-understanding of the surprising and unexpected properties of the solvent mixtures of this invention may be had "by'reference to Figure 2 of the patent drawings. In the graph presented-in Figure 2, the solvent rating has been plotted against the composition of the solvent mixture for Examples 3, 8, 12, 16,=and -20. Thejsolventrating is a'function-of the product yield and increase in aromatic concentration of the product. and is obtainedby means of the following arbitraryformula: I Solvent mang= ere1 0 yi'eldXf I 1 [octane number (produotfeed)] According to this formula, the best solvent will have the highest rating.

The broken line on the graph of Figure 2 represents the rating for mixtures of phenyl ethanol amine and diethylene glycol which would be expected from the solvent rating of the pure components. The solid line represents a curve which was drawn through the data actually obtained in Examples 12, 16 and 20. The surprising improvement in the solvent rating of the mixtures as compared to the rating which might have been predicted from a knowledge of the ratings of the pure ingredients is apparent.

Modifications of the procedure described herein for carrying out the method of this invention will be obvious to those skilled in the art, but this application for Letters Patent is intended to cover all such modifications as would reasonably fall within the scope of the appended claims:

The term consisting essentially of, as used in the ap pended claims, is not meant to exclude materials from the solvent mixtures which will not materially alter the properties of such mixtures.

We claim:

'1. A method of producing a hydrocarbon mixture en riched in aromatic content from a hydrocarbon feed mixture of lesser aromatic content comprisingthe step of extracting said feed mixture with a solvent mixture consisting essentially of diethylene glycol and phenyl ethanol amine in which said solvent mixture components are both present in amounts above 5% by volume so as to form a separable extract phase consisting of a mixture of hydrocarbons and solvent, and the step of separating an aromatic enriched hydrocarbon mixture from said extract phase.

2. The method of claim 1 in which said hydrocarbon feed mixture is a catalytically reformed heavy naphtha.

3. A method of producing a hydrocarbon mixture enriched in aromatic content from a hydrocarbon feed mixture of lesser aromatic content comprising the steps of extracting in an extraction zone said feed mixture with a solvent mixture consisting essentially of diethylene glycol and phenyl ethanol amine in which said solvent mixture components are both present in amounts above 5% by volume so as to form separable extract and rafiinate phases, separating said extract phase from said rafiinate phase, and fractionating said extract phase so as to separate said solvent mixture from the hydrocarbon mixture contained therein which is enriched in aromatic content.

4. A method of producing a hydrocarbon mixture en riched in aromatic content from a hydrocarbon feedmixture-of lesser aromatic content comprising the steps of extracting in an extraction zone said feed mixture with a solvent mixture consisting essentially of diethylene glycol and phenyl ethanol amine in which said solvent mixture components are both present in amounts above by volume so as to form separable extract and raftinate phases, separating said extract phase from said rafiinate phase, fractionating said extract phase so as to separate said solvent mixture from the hydrocarbon mixture contained therein which is enriched in aromatic content, and recycling said fractionated solvent mixture to said fractionation zone.

5. A method of producing a hydrocarbon mixture enriched in aromatic content from a hydrocarbon feed mixture of lesser aromatic content comprising the steps of extracting in an extraction zone said feed mixture with a solvent mixture consisting essentially of diethylene glycol and phenyl ethanol amine in which said solvent mix- .ture components are both present in amounts above 5% by. .volume so as to form separable extract and rafiinate phases, removing said extract phase from saidextraction zone and adding an appreciable quantity of heat to said extract, fractionating said extract to producevsaid hydrocarbon mixture enriched in aromatic content and to recover said solvent mixture," cooling said solvent mixture and recycling it to said extraction zone.

6. The method of claim 5 wherein said extract phase is heated and said'fractionated solvent mixture is cooled by passing them in heat exchange relation to each other.

7. A method of producing gasoline having an octane number at least above 100 from a gasoline having an octane number of 85, comprising the steps of introducing said octane gasoline into an extraction zone and extracting at a temperature of about 130 F. said 85 octane gasoline with a solvent mixture consisting essentially of approximately equal quantities of diethylene glycol and phenyl ethanol amine, the amount of said solvent mixture in said extraction zone being in the ratio of 2.3 volumes .of solvent mixture .to 1 volume of said 85 octane gasoline, so as to form separable extract and raffinate phases in said extraction zone, removing said extract phase from said extraction zone and adding an appreciable quantity of heat to said extract phase, fractionating said extract phase to obtain said octane gasoline and said solvent mixture, cooling said fractionated solvent mixture and recycling it to said extraction zone.

References Cited in the file of this patent 456,958 Great Britain Nov. 18, 1936 

1. A METHOD OF PRODUCING A HYDROCARBON MIXTURE ENRICHED IN AROMATIC CONTENT FROM A HYDROCARBON FEED MIXTURE OF LESSER AROMATIC CONTENT COMPRISING THE STEP OF EXTRACTING SAID FEED MIXTURE WITH A SOLVENT MIXTURE CONSISTING ESSENTIALLY OF DIETHYLENE GLYCOL AND PHENYL ETHANOL AMINE IN WHICH SAID SOLVENT MIXTURE COMPONENTS ARE BOTH PARESENT IN AMOUNTS ABOVE 5% BY VOLUME SO AS TO FORM A SEPARABLE EXTRA PHASE CONSISTING OF MIXTURE OF HYDROCARBONS AND SOLVENT, AND THE STEP OF SEPARATING AN AROMATIC ENRICHED HYDROCARBON MIXTURE FROM SAID EXTRACT PHASE. 